The invention is in the field of multiple photoflash lamp units, such as flashcubes and planar arrays.
U.S. Pat. Nos. 3,598,984 to Stanley Slomski and 3,598,985 to John Harnden and William Kornrumpf disclose a multiple flash array having first and second groups of flash lamps and reflectors facing in mutually opposite directions. The array is plugged into the camera whereby the first group of lamps faces frontwardly and is connected for the lamps of that group to be flashed. When these lamps have been flashed, the array is turned around and the lamps of the second group face frontwardly and are connected to be flashed. The lamps usually are flashed one at a time; however, a plurality of lamps can be flashed simultaneously if more light is desired.
The above-referenced patent application of Kurt Weber discloses a multiple flash lamp unit that can be connected to a camera in different orientations in each of which a different group of the flash lamps is relatively farther from the camera lens axis than are the other lamps of the unit. The lamps and electrical circuitry are arranged so that in any of the orientations of the unit with respect to the camera, only the group of lamps relatively farther from the lens axis can be flashed. The purpose of such an arrangement is to position the "active " group of flash lamps farther above the camera lens, in order to reduce the possibility of a "red-eye" effect that causes the pupils of a person's eyes to appear red or pink in flash pictures taken when the flash lamp is close to the camera lens.
The above-referenced Blount patent application discloses a multiple-group of lamp type of flash unit having an additional terminal for causing electrical shorting of the group of lamps that are not to be flashed in each orientation of the unit.
Each of the above-referenced multiple flash lamp units has, in a preferred embodiment, a plug-in connector tab privided with a plurality of electrical connection terminals in the form of conductive stripes printed on or otherwise attached to the connector tab. The various connector terminals are connected to individual lamps or to sequential firing circuitry interconnected with lamps in the unit. Such flash units, and particularly if they employ high voltage types of flash lamps which are flashed by a high voltage pulse (1000 or 2000 volts, for example) of low current energy, are prone to electrostatic firing of one or mor lamps if a connection terminal is touched by a person or object having an electrostatic charge. Such undesirable accidental flashing of lamps can also occur if the flash unit housing, which usually is made of a plastic material, acquires an electrostatic charge and a connector terminal is touched. The problem can also occur, and can be more severe, if both the plastic housing and the person or object touching a connection terminal are electrostatically charged with relatively opposite polarities.
The above-referenced Cote patent application discloses a terminal circuit arrangement for reducing the likelihood of accidental flashing of lamps by electrostatic charge when the terminals are touched while handling the unit. This is accomplished by making one of the terminals longer or otherwise more readily touchable than the others, and by connecting this more touchable terminal electrically in the unit so as to have more stray capacitance to ground than the other terminals.
Another way that a lamp can be undesirably and accidentally flashed is if there is a voltage across the socket contacts, when the unit is plugged into the socket, sufficient to flash a lamp. It is found that this can occur, for example, when the firing pulse source is a piezoelectric element connected electrically across the socket contacts and impacted in synchronism with opening of the shutter so as to produce a firing pulse for flashing a lamp. Arrangements of this type are disclosed in U.S. Pat. Nos. 2,972,937 and 3,106,080 to C. G. Suits. The piezoelectric element is impacted by a striker each time the camera shutter is actuated, whether or not a flash picture is being taken. If a flash lamp is connected across the piezoelectric element, it becomes flashed when a picture is taken. If a flash lamp is not connected across the element when a picture is taken, the element produces a voltage pulse (of 2000 volts, for example) when impacted, and the voltage across the element returns to zero value due to production of equal voltage of opposite polarity upon unstressing of the element when the impact pressure is released. However, it has been found that lamps will occasionally be flashed when the flash lamp, or mulitple flash lamp unit, it plugged into the socket after a non-flash picture has been taken. This is due to a residual or remanent voltage sometimes remaining in and across the piezoelectric element after a non-flash picture is taken. This is believed to occur because certain piezoelectric elements occasionally have a partial voltage breakdown while producing a voltage pulse, resulting in a retained residual voltage when the element is not loaded by a flash lamp. For example, assume that a non-loaded piezoelectric element is impacted and produces a voltage pulse of 2000 volts which is partially dissipated, due to a direct partial voltage breakdown or sparking or a partial corona discharge, to a value of 1000 volts, upon unstressing of the element after the impact, it will produce a reverse voltage of 2000 volts and thus will retain a residual voltage of 1000 volts of opposite polarity from the impact-produced pulse, and this residual voltage can remain long enough and at a high enough voltage to flash a lamp when the lamp or a unit containing the lamp is plugged into the socket.